Re: com port problem: it works on an Apple2, but not on a PC, why?

[kmccorm@access.digex.net (Kevin McCormick)]

In article <1993Jun23.215637.11124@julian.uwo.ca> wlsmith@valve.heart.rri.uwo.ca (Wayne Smith) writes:
>
>We have an old Searle ISO-CAP Gamma counter that outputs data through
>a serial line to an Apple ][.
>A basic program does the data collection, and the Apple's serial port is
>opened as 110 baud, 7 data bits, even parity, 1 stop (generic stuff).
>
>There are only 3 wires used: pins 1, 3 and 7.  Now, if this is standard
>RS-232, then pins 1 and 7 are ground and 3 is the receive data line.
>
>Now, I wired in a female 25-pin connector in parallel and connected it to
>a PC's serial port.  But with both the PC and the Apple running, the
>Apple gets data but the PC doesn't register anything. (it also doesn't
>work when connected to only the PC). 
>A diagnostic program verifies that the
>PC's serial port is working (although I haven't
>done an exernal loop-back test).  When a mouse is connected to the serial
>port I do get "garbage" when the mouse is moved, so the port seems to 
>function.
>
>Are there any differences between Apple ][ and PC serial ports that 
>can explain this situation?  ie does the Apple use a current-loop 
>rs-232?  I temporarily moved the wire on pin 3 to pin 2 on the PC, 
>but that didn't help.
>
>So, what do I have to do to get this to work on the PC?
>-Wayne-

Try wiring the one wire to pin 2 instead of 3.  Chances are one of the
computers is wired as a DCE, the other as a DTE.  The Apple receives on pin 3,
but the PC's trying to send on 3 and receive on 2.  If that still doesn't
work, then it's possible that the PC is looking for hardware-handshaking
signals that aren't present on the port.  Try disabling hardware-handshaking
and ignoring other signals (like DCD, DTR, DSR, etc...)

I hope this solves your problem!


-- 
Kevin McCormick                           | "The more we try to control, the
kmccorm@access.digex.net                  |  less we are really in control."
IRC: Xenophon                             |        - Robert J. Oppenheimer
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